Đáp án:

 a.

$\begin{array}{l}
C = {5.10^{ - 9}}\left( F \right)\\
q = {3.10^{ - 6}}\left( C \right)\\
E = {3.10^5}\left( {V/m} \right)
\end{array}$

b.

$\begin{array}{l}
C = 1,25,{10^{ - 8}}\left( C \right)\\
q = 7,{5.10^{ - 6}}\left( C \right)
\end{array}$

Giải thích các bước giải:

 a,diện tích bản tụ

$\begin{array}{l}
S = \pi {R^2} = \pi .0,{6^2}\\
C = \frac{{\varepsilon S}}{{{{9.10}^9}4\pi d}} = \frac{{1.\pi .0,{6^2}}}{{{{9.10}^9}4\pi {{.2.10}^{ - 3}}}} = {5.10^{ - 9}}\left( F \right)\\
q = CU = {5.10^{ - 9}}.600 = {3.10^{ - 6}}\left( C \right)\\
E = \frac{U}{d} = \frac{{600}}{{{{2.10}^{ - 3}}}} = {3.10^5}\left( {V/m} \right)
\end{array}$

b. coi tụ gồm 2 tụ mắc // 

$\begin{array}{l}
{C_1} = \frac{{{\varepsilon _1}S}}{{{{9.10}^9}4\pi d.2}} = \frac{{1.\pi .0,{6^2}}}{{{{9.10}^9}4\pi {{.2.10}^{ - 3}}.2}} = 2,{5.10^{ - 9}}\\
{C_2} = \frac{{{\varepsilon _2}S}}{{{{9.10}^9}4\pi d.2}} = \frac{{4.\pi .0,{6^2}}}{{{{9.10}^9}4\pi {{.2.10}^{ - 3}}.2}} = {10^{ - 8}}\\
C = {C_1} + {C_2} = 1,25,{10^{ - 8}}\left( C \right)
\end{array}$

$q = U.C = 600.1,25,{10^{ - 8}} = 7,{5.10^{ - 6}}\left( C \right)$